Vaccines are usually formulated with an adjuvant to enhance and improve the immune response, notably to prolong antibody response. For instance, Freund's adjuvant (Proceedings of The Society for Experimental Biology and Medicine, 1942, 49, 548-553), which corresponds to a solution of antigen emulsified in mineral oil, has first been used as an immunopotentiator or as an immunobooster. Freund's adjuvant forms a water-in-oil (WO) emulsion and exhibits an adjuvant effect essentially through a sustained release of the antigen.
Various other adjuvant systems have been evaluated in order to provide effective vaccines. These include, for instance, chitosan, cytokines, oligonucleotides, lipids, toxins, hapten carriers or aluminum hydroxide. In this regard, Matsumoto et al. (Avian diseases, 1971, 15, 109-117) has tested the efficacy of aluminum derivate such as aluminum hydroxide gel and chrome aluminum in vaccines. Blackall et al. (Avian Diseases, 1992, 36, 632-636) have compared aluminum-hydroxide adjuvant and WO emulsions. Squalene, saponin, Quil A, lipoidal amine, glycan or avridine have also been added as adjuvants to vaccines to improve their efficacy.
EP 0 640 348 relates to a vaccine comprising a WO emulsion and an immunostimulatory glycan. US 2014/0099358 proposes a vaccine comprising a water-in-oil emulsion and aluminum or a compound of aluminum or TiterMax (squalene). However, the design of combined emulsion-adjuvant systems generates safety issues because of possible side effects (Reid and Blackall, Avian Diseases, 1987, 31, 59-63). Furthermore, traditional WO emulsions often have a high viscosity and are difficult to formulate or inject.
Vaccines based on WOW emulsions have been tested in in ovo immunization of avian embryos (U.S. Pat. No. 5,817,320) and against specific viruses such as Newcastle disease virus, infectious bronchitis virus (Cajavec et al., Acta Veterinaria Hungarica, 1998, 46, 25-34), and infectious Coryza (Blackall, World's Poultry Science Journal, 1995, 51, 17-26).
Such vaccines in a WOW emulsion have also been improved in term of stability according to the nature and the proportions of the surfactants used to produce the WOW emulsion. In this context, Hunter and Bennet have studied the polyoxyethylene polyoxypropylene block copolymer of formula HO(C2H4O)b(C3H6O)a(C2H4O)b at Hydrophilic-Lipophilic Balance (HLB) below 2 (U.S. Pat. No. 5,622,649). They have also tested such WOW emulsions in vaccination methods for Hepatitis B infection and have mentioned their effectiveness against tetanus, malaria, AIDS, influenza and pneumococcal pneumonia.
Jiao and Burgess (AAPS Pharm. Sci., 2003, 5, 1-12) have evaluated the long-term stability of WOW multiple emulsions with respect to the concentrations of two specific surfactants, Span 83 and Tween 80, and have determined that a concentration ratio of 20% Span 83 and 0.1% Tween 80 provided the best long-term stability of WOW emulsions. WOW emulsions, however, do not always generate satisfactory immune response. In addition, WOW may be associated to a number of potential disadvantages including their lack of homogeneity, for instance in the size distribution profile of particles, and the possible viscosity of heterogeneous formulations. Furthermore, there is no established suitability of such systems for formulating large objects such as cells.
Accordingly, there is a need in the art for alternative, safe and improved vaccines, notably for use in animals.